The goal is to determine the role of the hippocampus in behavior, especially in behavioral arousal. Single cell activity will be recorded extracellularly in different regions of the hippocampus and related brain structures in freely behaving rats and rabbits. Rates and patterns of activity of different types of cells will be compared during different behavioral states, such as, slow wave sleep, paradoxical sleet, quiet awake, arousal from sleep, various depths of anaesthesia, as well as during orienting, consummatory and locomotor responses. Recording will be done during habituation and sensitization to various stimuli, during defensive reactions, such as freezing, fleeing, aggression and tonic immobility and during conditioning of defensive reactions to normally innocuous stimuli. The effects of lesions of hippocampal afferents and efferents on the animals' behavioral repertoire as well as on single cell activity during the above behaviors will be determined, as will the effects of stimulation of hippocampal afferents on cellular activity.